The invention relates to a quick-acting valve actuator, and also to a tool fitted with the actuator.
The field of application of the invention lies with valves for placing in a duct for sub-surface working, such as, for example, in wells for producing oil or gas, and any gushing well for extracting hydrocarbons present in the sub-surface, or any injection well.
As a general rule, production wells comprise an underground wall that is pierced for passing the fluid produced by the surrounding production bed into the inside of the well, so as subsequently to rise to the surface under drive from the pressure of the fluid that exists in said bed.
Thus, for the operator of the well, it is of great importance for a large quantity of production fluid to be taken from the well per unit time, i.e. for the production yield to be as high as possible. This production yield can be influenced by various parameters and conditions. One of these parameters, relating solely to the structure of the borehole, is the flow cross-section for the production fluid between the underground bed and the wall of the well. The greater this flow section, the greater the quantity of fluid that can be taken from the well. This flow section can become polluted by materials and fluids such as drilling mud, casing cement, or solid materials conveyed by the production fluid.
Nevertheless, it is difficult to know whether or not too small a production rate of fluid raised to the surface is due to the magnitude of the flow section between the underground layer and the well.
In order to evaluate the value of the flow section, it is known to monitor the pressure and the temperature that exist in the underground production layer. By closing and/or opening the valve situated between the surface and the production bed, through which valve the production fluid needs to pass in order to be raised to the surface, it is possible, starting from the measured temperature and pressure, to obtain information about the flow section at the underground layer, also known as its “skin”, and about its permeability.
By closing the valve suddenly, the pressure measured at the production bed is caused to pass from a production pressure P1 to a deposit pressure P2 that is higher, as shown in FIG. 1. Conversely, starting with a closed valve, when it is caused to open suddenly, the pressure measured at the production bed is caused to pass from the deposit pressure P2 to the production pressure P1.
The pressure measurement curves need to be used both in terms of value and also in terms of slope a as a function of time t. Thus, the time T taken by the measured pressure P to go from the production pressure P1 to the deposit pressure P2 is itself equal to a value lying in the range half a day to ten days.
In the event of opening and/or closing taking place quickly, the pressure curve approximates, at least during the initial stage immediately following full opening or closure, to a general first-order curve in response to a step in the flow rate and the valve, characteristic of the valve switching instantaneously between its closed state and its open state, or vice versa. Thus, a steep slope ax as presented by the curve of FIG. 1 indicates a skin that is thin or a flow section that is little obstructed, thereby leading to greater production yield.
It is then easy to deduce information therefrom relating to the fluid flow section at the production bed.
In contrast, if the opening and the closure of the valve are too slow, i.e. if the length of time that elapses between the valve being fully open and/or being fully closed is too great, then the pressure response approximates to a curve of order greater than one, such as the curve shown in FIG. 2, in which the slope of pressure as a function of time begins by increasing up to a point of inflection I, after which it decreases until the pressure settles down to steady conditions.
Under such circumstances, it is much more difficult to make any use of the curve of measured pressure P since it depends on various parameters in addition to the flow section at the production bed. Thus, the curve of measured pressure P is unusable for the time TI that elapses until the point of inflection I.
The invention seeks to obtain a valve actuator and a tool provided with the actuator that enables the valve to be opened and/or closed as quickly as possible between the last instant in which the valve is fully open and/or fully closed, and the instant in which the valve becomes fully closed and/or open, so that the flow rate measured downstream from the valve approximates as closely as possible to a step in the flow rate as a function of time, so that the response to valve actuation is as close as possible to the curve shown in FIG. 1.